VIENNA – The Organization of Petroleum Exporting Countries (OPEC) has opted to leave its oil-production quota of 28 million barrels of oil a day unchanged, even as some OPEC ministers “grow increasingly concerned over the plunging price of crude,” writes Dow Jones Newswires.

The news service notes that OPEC’s output in recent months has fallen by as much as half a million barrels below its target figure, as Venezuela and Nigeria are having trouble maintaining output, while Saudi Arabia is selling “all the crude for which it can find buyers.”

OPEC ministers “will now watch the market carefully for signs that the recent fall in crude prices may be turning into a rout,” notes the news source, adding that if prices continue to drop and buying slows, the cartel could decide to allow their output to “slip further” before the next OPEC meeting in December in Nigeria.

“Regardless of the quotas, the Saudis and others are always fine-tuning their output unofficially,” Michael Wittner, head of energy research at Calyon Corporate and Investment Bank, told the news source, adding that if crude oil prices fell towards $55 a barrel, “the Saudis will not wait for an official quota cut” to reduce output.

On Monday, oil prices fell below $65 a barrel for the first time in nearly six months before settling at $66.25 a barrel on the New York Mercantile Exchange (Nymex).

Meanwhile, the U.S. Energy Information Administration (EIA) reported on September 11 that the average national price of regular gasoline dropped from $2.727 a gallon on September 4 to $2.618 a gallon.